Gas burner nozzle

ABSTRACT

The invention relates to a gas burner nozzle for flame work, with a central oxygen supply consisting of several pipes ( 13 ) and with several pipes ( 11, 12 ) arranged around the aforementioned oxygen supply for the supply of fuel gas. According to the invention, the pipes for the oxygen supply are arranged in groups, with the individual groups arranged coaxially and at a distance from each other, and with each group consisting of at least two rows of pipes arranged in the form of concentric rings.

The invention relates to a gas burner nozzle for flame treatment operations, with a central oxygen feed which comprises a plurality of tubes, and with a plurality of tubes for a fuel gas feed which are arranged around the the oxygen feed.

Gas burner nozzles are used in flame treatment devices which are formed either as automatic devices or as hand-held flame treatment devices. Flame treatment operations are especially necessary for flame scarfing of slab surfaces. So, during the cooling of the slabs, which are produced by casting, unwanted cracks are frequently created on their surface which are removed by means of a surface treatment. The same also applies to burrs or whiskers which are created when machining the slabs, for example by cutting. The flame scarfing burners which are used are guided along the affected surfaces in order to remove the surface defects.

In the case of gas burner nozzles of the described type, there is the risk that during burner operation the flame flashes back. In order to prevent this, it has already been proposed to provide a porous element inside the nozzle body a long way behind the discharge orifice, which porous element is to form a safety barrier (cf. CH-A-472 632 or FR-A-1 448 292).

Furthermore, when flame scarfing by means of an oxygen jet of controllable output and orientation, which is enveloped by a heating flame, it is proposed in EP 0 043 822 [U.S. Pat. No. 4,373,969] to alter the cross section of the jet with regard to its shape and surface, independently of its output, during the course of the flame scarfing. The burner which is designed for this has an oxygen nozzle which is divided into a plurality of nozzles which are grouped adjacent to each other and as a compact bundle. This bundle of nozzles is surrounded by further nozzles which form in each case a burner for heating, wherein these nozzles and burners are provided with devices for individual feed with gas or oxygen, or a heating mixture. Each feed device can be individually controlled. As is apparent from the illustrated embodiment, 65 concentrically arranged oxygen feed tubes, with an equal distance to the adjacent tube in each case, are used, and which in turn are surrounded by 12 tubes with larger diameter in each case for heating gas feed. As a result of the controlling facility which is provided, effective burner cross sections are to be created, which are circular, rectangular or oval.

Furthermore, gas burners are known which have a plurality of tubes for an oxygen feed which are arranged coaxially to each other and which are surrounded by a plurality of tubes for a gas fuel feed which are arranged around them.

In the case of gas burners of the described type, according to the prior art diameters of the burners, which are circular in cross section, are customarily from 200 to 250 mm. This has the disadvantage that narrow sides of slabs have to be overtraveled many times with such burner nozzles. A simple enlargement of the burner diameter for example to 300 mm is in no way sufficient since the temperature would then be greatest in the center of the burner jet or burner jet cone on account of the greater heat and the melting on the workpiece would be correspondingly more intense than on the edge which in the case of longitudinally-guided burners leads to a surface which is concave in cross section. A further technical problem is the relatively high oxygen consumption.

It is therefore the object of the present invention to disclose a gas burner nozzle which with the lowest possible oxygen consumption and short machining time enables an optimum surface quality of the workpiece which is to be treated.

This object is achieved by a gas burner nozzle as claimed in claim 1.

According to the invention, the tubes for oxygen feed are not arranged equidistantly or on rings which are equal distances away from the center, but arranged in groups, wherein the individual groups are arranged coaxially and a distance apart from each other, and each group comprises at least two annularly arranged rows of tubes. In particular, three groups of tubes for oxygen feed are provided. In other words, 3 ring sections are preferably provided, which are a distance apart from each other and inside which individual tubes are arranged in each case, the distance from each other of which is less than the distance of the ring sections from each other. Rows of tubes for oxygen feed, which are arranged in 2 or 3 rings, can be associated with each group. Around the the tubes for oxygen feed, a group of nozzle orifices with smaller diameters in each case is provided on an outer ring, via which nozzle orifices the fuel gas is fed.

If a slab long side is overtraveled with such a nozzle, which has a diameter of 280 to 400 mm, then this can be treated in a single pass, wherein a slab surface has been created which is flat as far as possible. As a result of the repeated overtraveling of this long side being dispensed with, a saving of oxygen is already made to a significant degree. Surprisingly, an oxygen saving of about 25% per time unit additionally resulted, which is only possible by means of the newly created nozzle arrangement.

Each individual tube for oxygen feed preferably has an outlet inside diameter of 6 to 12 mm, especially 8 mm. As basically known according to the prior art, the gas burner has separate oxygen feed lines which can be separately controlled. In the present case, each separate gas feed is connected to a group of feed lines, i.e. to a ring section.

According to a further development of the invention, individual tubes of a group, preferably two to three tubes, are combined to form a sub-group which forms in each case a single-piece body which is arranged in the gas burner nozzle in an exchangeable manner. In this way, damaged surface sections on the end face can be partially renewed by exchange of affected sub-groups.

The the groups of tubes, according to a development of the invention, are arranged in a single end piece to which is connected a front block which has three pre-chambers for oxygen feed which are arranged coaxially to each other and connected in each case to the tubes of a (ring) group. By means of this measure, the gas burner nozzle weight can be considerably minimized. For service life reasons, the gas feed tubes are produced from copper.

The length of any tube is determined by the distance which is required in order to avoid turbulences at the far end of the tube which can lead to an explosion-like burn-out with corresponding nozzle damage. In particular, an optimum design of the individual tubes (preferably 8 mm wide at the outlet) has been created if each tube for oxygen feed is formed as a combination of a Laval nozzle with a cylindrical tube which is oriented toward the outlet. The Laval nozzle, which is known principally according to the prior art, has two cone-like sections, wherein the first cone, as seen in the flow direction, is formed in a converging manner and the cone which follows it is formed in a diverging manner. A cylindrical tube with constant diameter as far as the tube outlet is attached on the end of the diverging section.

From fluid dynamics it is known that with laminar flows in a tube, in which a constant pressure is applied, the flow velocity increases reciprocally to the reduction of diameter. As a result of the tube design, the gas flow which is guided within it is made to oscillate, wherein high-frequency impulse sequences are created on account of the interaction of the flow. The achievable impulse frequencies and also the amplitudes depend particularly on the inlet pressure, the degree of convergence, and the degree of divergence of the tube diameter, and also upon the length of the third section with a constant diameter. During flame scarfing, the shock-like impulses which leave the nozzle discharge end lead to liquid substances, which are created as a result of melting of the workpiece surface which is to be treated, and also solid particles, which are perhaps included, being blown away from the surface. This leads both to an increase of the surface quality of the treated workpiece, for example a slab surface, and to a further reduction of the oxygen consumption. Within the scope of the present invention, the diverging section can follow the first converging section of the inside cross section directly or by interposition of a section with constant diameter. As long as a section with constant diameter is present, the flow velocity in this section is maintained without superpositions occurring which are desired in the diverging section and in the extension tube which follows it. The short section with constant diameter should preferably be smaller than the respective lengths of the converging and of the diverging section in any case.

Further explanations for the present invention and also advantages are described with reference to the attached drawings. In the drawings:

FIG. 1 shows a plan view of a gas burner nozzle,

FIG. 2 shows a partial cross section through this gas burner nozzle,

FIGS. 3 a to d show cross sections in each case through a tube for oxygen feed with different gas flow structures.

The gas burner nozzle for flame treatment operations which is shown in FIG. 1 has a central oxygen feed section with a plurality of tubes which are arranged in groups. In the present case, the outer ring section 11 is formed by individual tubes, wherein the tubes 111 are arranged on an outer ring, the tubes 112 are arranged on a ring which follows next, and tubes 113 are arranged on an inner ring. The tubes 112 and 111 or 113 are arranged in each case with a “stagger” in an offset manner to each other. The tube diameter is 8 mm, and the tube distance of the tubes 111, 112 and 113 from the adjacent tube is about 4 mm in each case.

In the center ring section 12, two rows of individual tubes are arranged on different diameters and are also offset to each other so that a distance of 4 mm from the respectively next tube is established.

In the central ring section, 4 tubes are arranged in the innermost ring 4, and in the rings which follow it 12 tubes are arranged in each case. In the present case, this gives a total number of 148 tubes for oxygen feed. Tubes for fuel gas feed, which have a significantly smaller diameter, are located all around on two coaxially arranged rows 14 and 15. The entire nozzle head 10 consists of copper, wherein the gas burner nozzle can be formed as a solid body in which a corresponding number of holes have been manufactured.

In contrast, FIG. 2 shows a variant in which only an outer front section is solidly constructed, to which a front block is connected, in which a central oxygen feed 16 to the tubes of the ring group 13, a gas feed 17 which lies coaxially to this central oxygen feed and leads to the tubes of the ring group 12, and an outer coaxial gas feed 18 which leads to the group 11 of tubes, are arranged. Each of the three gas feeds 16, 17 and 18 can be separately controlled so that the gas velocity in the individual tubes can be correspondingly controlled.

Each individual tube, for example 111, 112, 113, is preferably formed in such a way that a cylindrical tube 101 with a length L_(K) is connected to a Laval nozzle 100 with the length L_(C). This Laval nozzle has a first converging section 121, which extends over a length L₂, and a diverging section 122, which has a length L₃. In between these the sections, a sub-section with a length L₄ can be arranged, which has a constant minimum diameter d_(min). The diameter of the cylindrical tube 101 is identified by d_(k) and has the size of the largest diameter of the cone-shaped divergence 122. The length L_(k) or L₅ can be varied, for example between the length measurements 72 mm, 65 mm and 25 mm. The length L₂ for example can be selected with 10 mm, the length L₄ with 2 mm, and the length L₃ with 25 mm. The gas which flows into the tube has a pressure P₀ of for example 1.3×10⁶ Pa and a temperature T₀ (for example room temperature). By variation of the pressure Po in relation to the outside pressure (environmental pressure), the jet cone of the discharging oxygen flow can be varied to form convergent, divergent or essentially parallel shapes. By means of the inlet pressure P₀, moreover, the differently resulting oscillation frequencies and oscillation amplitudes are varied. 

1. A gas burner nozzle for flame treatment operations with a central oxygen feed which comprises a plurality of tubes, and with a plurality of tubes for the fuel gas feed which are arranged around the oxygen feed. wherein the tubes for the oxygen feed are arranged in groups in each case, wherein the individual groups [[(11, 12, 13)]] are arranged coaxially and a distance apart from each other, and each group [[(11, 12, 13)]] comprises at least two annularly arranged rows of tubes.
 2. The gas burner nozzle as claimed in claim 1 wherein there are three groups [[(11, 12, 13)]] of tubes for oxygen feed.
 3. The gas burner nozzle as claimed in claim 1 wherein each individual tube for oxygen feed has an outlet inside diameter of 6 to 12 mm.
 4. The gas burner nozzle as claimed in claim 1 wherein each group of feed lines has a separate gas feed control facility.
 5. The gas burner nozzle as claimed in claim 1 wherein individual tubes of a group are combined to form a sub-group which form in each case a one-piece body which is arranged in the gas burner nozzle preferably in an exchangeable manner.
 6. The gas burner nozzle as claimed in claim 1 wherein the groups of tubes are arranged in an end piece which is connected to a front block which has three pre-chambers [[(16, 17, 18)]] for oxygen feed which are arranged coaxially to each other and connected in each case to the tubes of one of the groups [[(11, 12, 13)]].
 7. The gas burner nozzle as claimed in claim 1 wherein the gas feed tubes consist of copper.
 8. The gas burner nozzle as claimed in claim 1 wherein the outside diameter is 250 to 400 mm.
 9. The gas burner nozzle as claimed in claim 1 wherein each tube for oxygen feed is formed as a combination of a Laval nozzle [[(100)]] with a cylindrical tube [[(101)]].
 10. The gas burner nozzle as claimed in claim 9 wherein the length [[(L₂)]] of the first section [[(121)]] is shorter than the length [[(L₃)]] of the second section [[(122)]] and/or of the third section [[(123)]].
 11. The gas burner nozzle as claimed in claim 1, wherein the diameter of the three sections, and also their lengths, are matched to each other so that the gas flows out at the nozzle discharge end in pulse form.
 12. The gas burner nozzle as claimed in claim 11 wherein the impulse frequency at the nozzle discharge end is 100 to 650 Hz.
 13. The gas burner nozzle as claimed in claim 1 wherein the maximum gas flow velocity in each tube is Mach 2 [[(equal to twice the speed of sound)]]. 